It has been widely established that very significant increases in animal feeding efficiencies can be obtained by the use of certain feed additives. This has been particularly true in the feeding of monogastrics where it is now the usual practice to supplement the diet with such materials as amino acids. The amino acids represent a particularly useful group of additives since they are the units from which protein molecules are constructed. Although many biologically active materials are employed as feed additives, it is recognized that many of these are inefficiently utilized by ruminants due to degradation thereof in the rumen. Thus, materials such as amino acids and vitamins are not used routinely in ruminant feeds because of their susceptibility to ruminal degradation.
The rumen, which is essentially a continuous fermenter, supports a variety of micro-organisms under neutral conditions (pH=5-8) which attack and digest much of the feed as part of their normal life cycle. The rumen micro-organisms use the feed to synthesize microbial protein. A stream of ingesta, rich in microbial cells, passes out of the rumen into the omasum. The function of the omasum is to separate liquids and solids. Much of the liquid reenters the rumen while the remainder of the material enters the abomasum or true stomach. Digestion and absorption then proceed in the abomasum in a manner similar to that found in monogastrics. Enzymes secreted into the lumen of the abomasum digest much of the material, including some of that contained in the microbial cells.
The rumen has the great advantage of being able to convert by microbial action many feed components which have no direct nutritive value for the host into products which can be assimilated and utilized by the host. For example, urea may be converted to microbial protein which subsequently may be digested and utilized by the host animal. Cellulose may be converted to a mixture of volatile fatty acids which can serve as a source of energy to the host.
Unfortunately, this microbial action also presents certain disadvantages. For instance, soluble proteins of high nutritive value may be digested and deaminated in the rumen and in part resynthesized into microbial protein of lower nutritive value. Amino acids, the units from which protein molecules are constructed, are also chemically changed by the rumen microorganisms which convert amino acids to carbon dioxide, volatile fatty acids, and ammonia.
It is well recognized in the art that this microbial activity of the rumen limits the productivity of ruminants. Consequently, a great deal of effort has been expended towards providing a bioactive substance in a form which will pass through the rumen essentially unaltered, yet undergo disintegration and absorption in the abomasum.
Numerous patents disclose coating bioactive substances with material which survives the rumen but degrades in the abomasum. For example, Ando U.S. Pat. No. 4,713,245 discloses a rumen-surviving granule comprising a core of bioactive material, a coating substance stable at neutral pH (as found in the rumen) but dissolved or disintegrated at pH=3 (as found in the abomasum), and at least one other coating selected from the group consisting of fatty acids having at least 14 carbon atoms and waxes, animal fat, and vegetable fat having a melting point of 40.degree. C. or higher.
Autant U.S. Pat. No. 4,832,967 discloses a two-layer rumen-surviving coating for water-soluble bioactive substances. The resulting particulate is stable at pH at least as high as 5.5, and releases bioactive substance at pH of 3.5 or less. The coating medium comprises a first coating layer consisting of material sensitive to pH variations and a second coating layer consisting of a hydrophobic composition which must include inorganic filter if the bioactive core has not undergone a surface treatment (application of hydrophobic binder). This hydrophobic outer coating layer is provided with a texture which permits diffusion or penetration of the external liquid medium. The outer coating preferably contains a mixture of hydrophobic substances.
Autant U.S. Pat. No. 4,876,097 discloses a coating composition which is stable at pH less than or equal to about 3.5. The coating comprises a film-forming, water-insoluble binder which contains a substance which controls hydrophilicity, and optionally a substance which is sensitive to pH. Both waxes (hydrophobic) and propylene glycol (water-soluble) are suitable for controlling the hydrophilic/hydrophobic balance. Controlling the hydrophilicity of the particle is said to limit release of the bioactive material in neutral or slightly acidic media, i.e., in the rumen. In very acidic media, i.e., the abomasum, pH-sensitive fillers are activated by the media, which diffuses slowly at a rate established by the hydrophilicity of the coating. The resulting dissolution or swelling of the pH-sensitive filler degrades the coating and releases the bioactive material.
Sibbald U.S. Pat. No. 3,541,204 discloses hydrogenated vegetable and animal fats and waxes such as rice bran wax as coatings which survive the rumen but are disrupted in the intestinal tract.
One well recognized problem with such coatings that can survive the environment of the rumen is that the coated granules tend to float on the contents of the rumen. If the capsules or granules float for a sufficient period, they will be regurgitated. Regurgitation increases the likelihood that the coating will be compromised or destroyed during rumination. Consequently, many of the above described patents provide for adjustment of the density of the capsule or granule by addition of a high density weighting agent, to ensure that the granule sinks. However, as disclosed by Sibbald, the density must not be so great that the capsule will sink to the floor of the rumen and remain there indefinitely. Sibbald discloses an adjusted density of 0.8 to 2.0, preferably about 1.0 to 1.4, g/cc.
However, the art has not recognized that particles coated with hydrophobic material will float on water (and no rumen), even though the particles have been densified to a specific gravity greater than that of water (or rumen). Rather, the art teaches that densification alone provides the proper particle/fluid interaction and precludes undesirable floatation of particles.